1. Field of the Invention
This invention relates to a recording medium and a recording method, more particularly to an improved recording medium which can provide various characteristics such as excellent color forming characteristic, ink dot shape, etc., and an ink jet recording method by use of said recording medium.
2. Related Background Art
Ink jet recording performs by generating small droplets of recording liquid (hereinafter called ink) using discharging systems (e.g. electrostatic attraction system, the system of giving mechanical vibration or displacement to ink by use of a piezoelectric element, the system in which pressure formed when ink is foamed by heating), permitting them to fly and attaching a part or whole thereof onto a recording medium such as paper. This method is now attracting attention as a recording method which minimizes generation of noise and is capable of performing high speed and multicolor printing.
As an ink for ink jet recording, there have been primarily used an aqueous type ink for the reasons of safety and recording characteristics, while as a recording medium, normal paper has been generally used in the prior art. When performing recording on such paper with a liquid ink, it is generally required that printed letters should not become unclear by blurring, and it is also desirable that the ink after recording should be dried as soon as possible to avoid unexpected contamination of the paper surface.
Particularly, in the multi-color ink jet recording system which use inks of two or more different colors, various requirements as set forth below should be satisfied.
(1) Even if a first ink is absorbed rapidly onto a recording medium, an ink attached later should not be mixed with the ink previously attached, or should not disturb the ink dot or should not flow out.
(2) The diameter of the ink dot may not become greater than required due to diffusion on a recording medium.
(3) The shape of an ink dot should be approximate to a true circle, and its circumference should be smooth.
(4) The density of an ink dot should be high, enough to retain its clear circumference.
(5) The whiteness of a recording medium should be high enough to give good contrast of an ink dot as formed.
(6) The color of an ink should not be affected by a recording medium.
(7) The dimensional fluctuation of a recording medium (e.g. wrinkle, elongation) should be minimal before and after recording.
(8) The recorded image should have sufficient resistance to water, oxidative gas in the air and light.
(9) Power dropping off from the coated layer of a recording medium or a substrate should be kept minimum, etc.
In order to satisfy these requirements, there have been made several proposals in the prior art. For example, for improvement of ink absorptivity or blurring of ink dots, Japanese Laid-Open patent application No. 49113/1978 discloses an ink jet recording paper comprising a sheet made of wood pulp impregnated with a water-soluble polymer. As examples of coated paper, Japanese Laid-open patent application No. 5830/1980 discloses an ink jet recording sheet having an ink absorptive coated layer provided on a support, and Japanese Laid-open patent application No. 11829/1980 an ink jet recording sheet comprising two or more layers with different ink absorptivities on paper which is not sized, respectively. Further, the ink jet recording medium disclosed in Japanese Laid-Open patent application No. 99693/1981 obtains water resistance by containing a quaternary ammonium halide, etc.
Also, there is proposed a paper containing synthetic amorphous silica as an ink jet recording medium. This recording medium, while having the advantage of, e.g., excellent color forming characteristic of a recording agent as an ink jet recording medium, has non-uniform shapes of such silica particles and wide distribution of particle sizes thereof, and therefore involves the inconvenience that, when ink absorptivity is intended to be improved, the coated layer strength is lowered to generate powder drop-off. Particularly, powder drop-off from the coated layer of the recording medium or the substrate causes non-discharging of ink through clogging of nozzles, whereby reliability of a recording device will be undesirably lowered.
Also, Japanese Laid-open patent application No. 146889/1984 discloses a non-coated type of ink jet recording paper in which synthetic amorphous silica is internally added as the loading material.
Such recording paper, while having the advantages of, e.g., improvement of dot shape as well as optical density as compared with recording papers containing loading materials generally employed such as clay, talc, calcium carbonate, etc., does not have satisfactory characteristics for uses in which high image quality is demanded.
Accordingly, an object of the present invention is to satisfy the various tasks which could not be solved by the prior art in the field of art as described above, particularly to provide a recording medium which can satisfy various demands as mentioned above, particularly which can improve color forming characteristic, optical density and dot shape in recording of color images by use of a plural number of color inks according to the ink jet recording system and an ink jet recording method by use thereof.
Another object of the present invention is to provide a recording medium which can satisfy, at the same time, the requirements for color forming characteristic, ink absorptivity and coated layer strength.